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To monitor network latency and throughput for IBM Z workloads, collect measurements at the layer where the symptom appears: session response times for user-facing delay, TCP/IP and interface statistics for connection or transfer behavior, packet traces for protocol-level diagnosis, and OSA data when adapter behavior is in question. z/OS Communications Server provides Network Management Interfaces (NMIs) and SMF data for TCP/IP and VTAM activity; IBM Z OMEGAMON Network Monitor can collect performance data across monitored LPARs.
Choose measurements that match the symptom
Latency and throughput are not single counters. A slow interactive session, a sluggish file transfer, packet retransmissions, and an overloaded host interface can look similar to a user but require different evidence. First identify the affected service, time window, LPAR, TCP/IP stack, and workload pattern. Compare measurements with a baseline taken under comparable conditions before attributing a change to configuration or hardware.
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| Question | Useful data | Best fit |
|---|---|---|
| Are users seeing slow TN3270 sessions? | TN3270E connection performance and response-time data | Session-level latency investigation |
| Are connections or transfers behaving poorly? | TCP connection activity, UDP endpoint activity, and TCP/IP interface or global-stack statistics | Connection and stack-level investigation |
| What is happening at protocol level? | Real-time TCP/IP packet, OSAENTA, or data traces | Focused troubleshooting that needs packet detail |
| Is the concern related to VTAM networking? | VTAM Enterprise Extender (EE) and High Performance Routing (HPR) information | VTAM and network-resource investigation |
| Could adapter behavior be involved? | OSA adapter information and configuration, interpreted alongside stack measurements | Host-interface and adapter investigation |
These data types are available through Communications Server NMIs and related monitoring sources; IBM documents real-time traces, connection and endpoint activity, interface statistics, TN3270E performance, and VTAM EE/HPR information in its z/OS 3.2 Network Management Interfaces reference.
Start with z/OS Communications Server data
Use the NMI or existing monitoring and SMF infrastructure to collect the evidence suited to the question. NMIs provide programmatic access to TCP/IP and VTAM processing; relevant data can also be available through SNMP MIBs, command displays, VTAM Performance Monitor Interface (PMI), and traditional SMF services, depending on the metric and collection setup.
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If you build a custom NMI collector, account for an important deployment constraint: the documented network-management clients must run on the same z/OS image as Communications Server. A collector on another image cannot simply serve as the NMI client for that stack.
Use packet tracing only when packet-level detail is needed to answer a specific diagnostic question. IBM documents the trace capabilities, but does not establish a universal sampling rate or retention period; set those according to the incident, storage capacity, and operational requirements.
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Enable the data needed for session response time
Some measurements require configuration before an incident. IBM’s OMEGAMON Network Monitor setup guidance calls for enabling the applicable Communications Server interfaces on each monitored system. For FTP and TN3270 monitoring, configure NETMONitor SMFService in the TCP/IP profile. TN3270 response-time collection also requires an applicable MONITORGROUP in the Telnet profile; IBM’s example specifies the AVERAGE and BUCKETS characteristics.
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Use OMEGAMON for managed multi-LPAR collection
IBM Z OMEGAMON Network Monitor collects TCP/IP and VTAM performance data for managed environments. Its documented coverage includes TCP/IP address spaces, TN3270 sessions, HPR and EE connections, FTP sessions and transfers, OSA adapters, TCP/IP connections and interfaces, gateways, CSM, VTAM buffer pools, and the VTAM environment. Its agent runs on every LPAR being monitored and uses NMIs, SNMP MIBs, and VTAM PMI as data sources.
Capacity-plan the agent in the context of the deployment: IBM notes that data-space use varies with the number of address spaces, monitored resources, and configured collection types. Observe actual overhead and adjust collection scope to the value of the data. IBM’s overview explains how real-time data is collected.
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Investigate OSA and configuration effects carefully
If measurements point toward adapter or interrupt behavior, consult documentation that matches the installed z/OS release and OSA hardware. IBM describes optimized latency mode for OSA-Express QDIO as adjusting inbound and outbound interrupt processing to reduce latency and potentially increase throughput for high-volume, interactive, non-streaming workloads. That description is not a guarantee of improvement for every workload; confirm applicability and exact configuration syntax in the release-specific IP Configuration Guide before making a change.
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Compare collection approaches before expanding monitoring
- Data scope: Decide whether the need is session, connection, interface or stack, packet, or VTAM-resource visibility.
- Time horizon: NMIs and traces support real-time observation; SMF-backed collection can support event and historical analysis.
- Deployment: Custom NMI clients run on the same z/OS image as Communications Server, while OMEGAMON places an agent on every monitored LPAR.
- Operational cost: Balance data-space use and trace detail or volume against the diagnostic value the team needs.
No single monitoring method establishes a universal latency or throughput expectation for IBM Z. IBM’s z/OS Communications Server Performance Index points to release-specific performance reports; interpret any published result in the context of its workload, hardware, and test conditions rather than treating it as a general platform benchmark.
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